[libstdc++-v3] Remove std::construct and std::destroy

[Benjamin Kosnik]

Note this discussion is only relevant for the trunk, not branch.

Ok, to sum up this thread, I think it's ok to move deprecated/old bits to 
backward headers, but not remove them entirely from the library. In 
addition, deprecated features and constructs should not be used 
internally in the library.

Stephen, does this make it clear what the course of action should be?

thanks,
benjamin